The present embodiments relate generally to devices primarily for use in semiconductor wafer processing equipment having an aluminum nitride coating provided thereon. More particularly, the embodiments relate to heating units, wafer carriers, and electrostatic chucks having a coating applied thereon having a plurality of zones of differing resistivities.
In one application, the wafer processing apparatus is especially useful as an heated electrostatic chuck for applications where a semiconductor wafer needs to be heated from 100-600° C. while it is electrostatically clamped to the surface of the heated chuck. The chucking force is achieved when the resistivity of the layer between the chucking electrode and the wafer falls within a range defined as the Johnson-Rahbeck regime (See FIG. 7). The current invention allows for the bulk resistivity of the said layer to be tuned to fall within the Johnson-Rahbeck regime at a given temperature range.
Prior art electrostatic Johnson-Rahbeck chucks using aluminum nitride materials are used for room temperature chucking applications, and are not used at higher application temperatures of 150-500° C. That is because these prior art chucks typically have polymeric or silicone adhesives that do not survive the high temperature applications.
Also in the prior art there have been high temperature Johnson-Rahbeck chucks available, such as carbon-doped pyrolitic boron nitride chucks by Advanced Ceramics Corporation (such as detailed in U.S. Pat. No. 45,748,436), or other pyrolitic boron nitride chucks doped with other materials such as silicon, as shown in U.S. Pat. No. 5,663,865 to Shin-Etsu Chemical Co. Such chucks however are cumbersome to fabricate due to the strict control of the dopant levels in the pyrolitic boron nitride.
In addition, some heated electrostatic chucks have been disclosed where a bulk sintered ceramic substrate is used with a heating element embedded in the core. The temperature of these types of substrates however cannot be ramped very quickly, because the embedded electrode acts as a defect from which cracks can initiate when thermally ramping at substantially high rates (e.g. >10° C./min). Heated substrates with a layered electrode on a surface of the substrate do not suffer from this limitation and ramp rates well over 20° C./min (up to 300° C./min) have been measured.
An important property of a film coating on the outer surface of a wafer processing apparatus is its resistance to corrosion when exposed to halogen plasma environments. Due to its high resistance to corrosion when exposed to halogen plasma environments, aluminum nitride has become the state-of-the-art material for fabrication of high-temperature wafer processing supports.
Typical resistivity values for AlN films range from 1011 to 1014 ohm-cm and drop by approximately a factor of 20 per 100° C. temperature increase. Thus, in high-temperature applications the resistivity of these AlN films drops sufficiently low to allow excessive leakage current between high and low electrical potential segments of the electrode path, or between the heating electrode and any electrically conductive films deposited onto the AlN during wafer processing, or between the electrode and the wafer itself. This leakage current limits the useful temperature range of a wafer heating apparatus. The AlN film can be replaced by materials with higher electrical resistivity, however, the resistance to halogen plasma may be diminished. As processing temperatures creep higher, there is a need for films with higher resistivity than AlN, which still maintain the excellent corrosion resistance. The current invention provides a method of modifying the bulk resistivity of a film coating while maintaining the excellent corrosion resistant properties of typical AlN films, thus allowing higher useful operating temperatures. It uses a film coating having different regions of differing resistivities. Thus, the bulk resistivity of a film at a given temperature can be modified by simply changing the relative amount of each region present in the film, without having to formulate new film materials to produce chucks having different bulk resistivities at a certain temperature.
The heaters, electrostatic Johnson-Rahbeck chucks, and wafer carriers of the present embodiments meet the needs of maintaining a desired bulk resistivity at high temperatures, are relatively easy to fabricate, are capable of being thermally ramped at substantially high thermal ramp rates, and furthermore, where electrostatic chucking is desired, provide clamping at high power at relatively low voltages.